Modern day Tokyo. A bustling region with a ridiculous number of residents, this center of cultural development is practically Japan's answer to America's New York. People of all ages and walks of life scurry about on their busy way day in and day out. It's very much a microcosm of the human race. It is in this region, specifically, that an odd occurrence has begun. At midnight every night, the world turns to a sickening shade of green, normal humans morph into the shapes of coffins, and strange creatures called Shadows wander about, seeking prey. Only a select few are capable of being active during this time, and among those, not all have the capabilities of resisting the Shadows.
The ones that do, however, awaken to the power of Persona.
To those that can experience that hidden "Dark Hour", it's clear that there is something dreadfully wrong with Tokyo. Strings of disappearances, and strange sightings, reported on the news suddenly seem a little more worrying in hindsight. These few can not only experience that hidden hour, however, but they can see the hidden portals connecting our normal world to a foreign plane. Roughly the same on a structural level, this "Dark World" is a distortion and mockery of the world humans call home, with beings of mythology and legend- demons- wandering freely.
Yes, something is entirely wrong in Tokyo, and it's up to you Persona-users to find out what.